v. i6 RECEPTORS OF ELASMOBRANCHS 171 



relatively slow. If the whole eye is cut out from the head, in the dark, 

 the sphincter, being an independent effector, still closes when illumi- 

 nated. The muscle, being without nerves, is not affected by any of the 

 usual drugs that mimic action of the autonomic nervous system, 

 though some of these affect the innervated dilatator muscle. We have 

 therefore the curious situation that no 'autonomic' drugs applied to 

 the isolated dark adapted eye cause closure of the pupil ; this can only 

 be produced by illumination (Fig. 108). 



The ear of elasmobranchs contains receptors concerned (1) with 

 maintenance of muscle tone, (2) with angular accelerations, (3) with 



Red 



Red 



White 



Adrenaline j//00,000 



Minutes 



Fig. 108. Movements of margin of pupil of an isolated iris of the shark Mustelus, 

 followed by plotting with a camera lucida and here shown magnified 53 X . Addition 

 of adrenaline causes slight dilation of the already dilated pupil and illumination then 

 causes closure. Acetyl choline even in concentrations of 1 in 10,000 has a similar 

 dilatory effect. (From Young, Proc. Roy. Soc. B. 112.) 



gravity, (4) perhaps with hearing. There are three pairs of semi- 

 circular canals, each with an ampulla containing receptor cells, whose 

 hairs are embedded in a gelatinous cupula. This behaves as a highly 

 damped torsion pendulum, swinging with movement of the fluid. 

 These receptors discharge impulses continuously and during angular 

 rotations the frequency is either increased or decreased in the appro- 

 priate ampullae, initiating compensatory movements of the eyes and 

 fins. 



The otolith organs include three patches of receptor cells in par- 

 tially distinct sacs, the utricle, saccule, and lagena. The endolym- 

 phatic duct is an open canal and in some species serves to admit sand 

 grains, which are attached to the maculae as gravity receptors. The 

 utricle seems to be the main receptor producing appropriate postures 

 in relation to gravity. The lagena shows a maximum discharge rate 

 near the normal position of the head and thus serves as an 'into level' 

 receptor. The areas of these maculae that carry otoliths do not 

 respond to vibrational stimuli but carry only gravitational receptors. 

 Vibration responses in the form of nerve impulses have been seen 

 in rays but only up to 120 c/sec, although vestibular microphonics 

 up to 750 c/sec occur. At high intensity there is much synchronization 



